Method and apparatus for fixing the location of a fixed wireless terminal in a wireless network

ABSTRACT

A method for fixing a location of a fixed wireless terminal. The method includes receiving a first plurality of telecommunication signals at the fixed wireless terminal, generating a first model of a network environment of the fixed wireless terminal based on the first plurality of received signals, receiving a second plurality of telecommunication signals at the fixed wireless terminal, generating a second model of the network environment of the fixed wireless terminal based on the second plurality of received signals, and determining whether the first and second models differ beyond a predetermined limit. The network environment models may be generated according to identification codes sent with each of the plurality of received signals, such as digital verification color codes, digital color codes, or supervisory audio tones. The network environments may also be generated according to the received signal strengths of the received signals or the time difference of the received signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field on Invention

The field of the present invention relates generally to wirelesstelecommunications and, more particularly, to methods and apparatusesfor fixing the location of a fixed wireless terminal in a wirelessnetwork.

2. Description of Background

Throughout the world, there exist places where conventional landlinetelephone service is unavailable or inadequate. In addition, it istypically expensive and time-consuming to build a wireline network. Inrecent years, however, wireless telephone service has proliferatedthroughout the world, including places that never offered landlineservice. Wireless service can support many potential customers withoutthe capital expenses associated with digging up streets and wiring olderbusiness districts. Installation of a wireless network can beaccomplished in a matter of months, rather than the years associatedwith installing a wireline network. Thus, many locations around theworld that do not have an embedded wireline network or have aninadequate wireline network are seeking to implement wireless solutions.

Wireless service, however, is generally more expensive than equivalentwired service. Wireless service providers generally believe that mobileflexibility demands a premium service charge and, unlike a dedicatedwireline network, wireless customers share a limited resource—RFspectrum bandwidth. Thus, wireless service providers typically offerusage-sensitive pricing, which has a tendency to control access to thewireless network and limit wasteful use. Wireless service users inlocations with no or inadequate landline service, however, perceive thatwireless service should be offered at rates competitive to wirelinenetworks.

As a result, some wireless service providers offer fixed wirelesssolutions in these locations at a discount over mobile wireless service.Offering fixed wireless service at lower rates than mobile wirelessservice presents the technical dilemma of differentiating betweenregular mobile wireless users and fixed wireless users. The typicalfixed wireless system includes a fixed wireless terminal for interfacinga fixed wireless user's telephone unit with a mobile switching center(MSC). The fixed wireless terminals are preferably confined to a fixedlocation, such as mounted to the side of a user's residence or equipmentrooms, basements, attics, and closets, within the geographic areaserviced by the fixed wireless network. However, because the fixedwireless terminal is essentially a wireless device, it may simply beremoved from its fixed location and thus become a de facto mobiletelephone interface.

A variety of solutions have been offered to prevent misuse and abuse offixed wireless systems. One prior solution has been to offer specificlocation or home-zoning pricing plans, in which, for example, callsoriginating from and terminating at a particular cell site are subjectto a fixed wireless rate, and calls which do not originate and terminateat the particular site are subject to the mobile rate. Home-zoningplans, however, are difficult to implement, especially in urban areas,where cell configurations may periodically change during periods of highwireless volume. Moreover, such a solution is relatively expensive toimplement, in part because the existing billing system would have to berewritten to support the functionality.

Another suggested solution is to incorporate Global Positioning System(GPS) receivers into fixed wireless terminals to generate accuratereadings with respect to the physical location of a user. That solution,however, would require that the hardware and software supporting the GPSsystem be installed in all terminals, and thus would likely increase thecost of the terminal.

Another prior solution involves installing a motion detector, such as amercury switch, in the fixed wireless unit. The motion detector is incommunication with a controller for the fixed wireless unit, andinstructs the controller to disable the unit when motion is detected.Such a system, however, is susceptible to tampering or sabotage whichmay render the motion detector nonfunctional.

Many other attempts have been made at restricting or controlling accessor determining location of a wireless terminal. For example, it is knownto restrict call setup by defining a fixed subscription area (FSA) inthe mobile switching center (MSC). Any attempts by the subscriberterminal to access the system will be denied or redirected to accesseswithin the FSA. This prohibits significant movement of the fixedsubscriber, but allows normal subscriber access within, near, orslightly outside of the cell coverage area of the FSA. The majordisadvantage with this method or any system based on the method is thatextensive changes are required in the MSC operating software. Inaddition, a method specifically designed to support TDMA wireless fixedoperation is known which involves changes to the MSC operating softwareby defining a location area identity (LAI), not unlike the FSApreviously described. The switch maintains a list of handover candidatesfor the fixed wireless terminal. Any time the terminal moves beyond thefixed area, a handover is attempted to one of the handover candidates.Further, a timing advance (TA) value is maintained for each cell in thecandidate list. This TA value is essentially a compensation value forthe round trip time of a signal from the base station to the wirelessterminal. If the TA value for the home cell or any handover candidatecell is out of range of the stored value, a violation signal is sent tothe system operator. Further call termination is possible.

Other more complex and accurate solutions have been developed. Forinstance, it is known to determine the location of a wireless terminalby measuring the relative time of arrival of a single data packettransmitted by each of three independent transmitting antennas. Becausethe locations of the antennas are known, the receiver can compute itsown location. Again, however, such a method requires extensive systemchanges to support the transmission of the data packets by three basestations or, at the very least, three spatially diverse antennalocations.

According to another known method of determining the position of asubscriber terminal, a mobile unit utilizing a plurality of rangetransceivers located at known fixed locations are adapted to transmitapproximately synchronized digital range signals. This system appears tomimic the functionality of the global GPS system, although implementedwith frequencies assigned to the wireless provider.

The above-described solutions, though all plausible for locationdetermination, are not entirely suitable for a simple fixed wirelessdevice location fixer. They all require extensive system modifications.They all require extensive changes to the MSC operating software or tosome ancillary devices. Another disadvantage of the latter two solutionsis they not only require extensive system development, but they alsorequire frequency spectrum, a quite valuable commodity.

Therefore, there exists a need for a method and apparatus to fix thelocation of a fixed wireless terminal which eliminates the need foradditional hardware and installation expenses. There also exists a needfor a method and apparatus to fix the location of a fixed wirelessterminal which would reduce the likelihood tampering, sabotage, andfraud.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a practical implementation for fixing thelocation of a fixed wireless terminal based on telecommunicationsignals, such as signals received from base stations of a fixed wirelessnetwork. The signals are received on one or more channels and are usedto construct models of the network environment of the fixed wirelessterminal at different times, such as periodically or each time theterminal is used. The most recent model is compared to one or moreprevious models to determine if the fixed wireless terminal has changedlocations, i.e., if it is mobile. The models may be constructed from oneor more features of the received signals.

According to one embodiment of the present invention, the networkenvironment models are constructed from identification codes sent witheach of the signals. The identification codes are typically transmittedwith telecommunication signals in a mobile telecommunications network toensure that a mobile telecommunications device is communicating with theproper base station. For example, in a digital network, a digitalverification color code (DVCC) is typically sent with all signals ondigital control channels. According to another embodiment, models areconstructed from digital color codes and their corresponding analogcontrol channel or supervisory audio tones and their correspondinganalog voice channel.

According to another embodiment, the present invention generates networkenvironment models based on the strength of the receivedtelecommunications signals. According to yet another embodiment, thepresent invention monitors a time of arrival of signals received fromdifferent base stations to generate the network environment models.

If the most recent model and a previous model of the network environmentsufficiently match, the present invention assumes that the location ofthe fixed wireless terminal has not changed. Conversely, if the modelsdo not sufficiently match, the present invention assumes that thelocation of the fixed wireless terminal has changed and that, therefore,the fixed wireless terminal is mobile. If the fixed wireless terminal ismobile, the present invention may prevent a user from accessing thenetwork via the fixed wireless terminal for a period of time, such astwenty-four hours. To ameliorate such potentially harsh ramifications,the present invention may be programmed to only prevent access to thenetwork if the fixed wireless terminal is determined to be mobile on aspecified number of occasions within a certain time period. Moreover,the present invention may be programmed to nevertheless permit access tothe network for identifiable emergency purposes even if access would beotherwise prevented.

Thus, the present invention fixes the location of a fixed wirelessterminal and prevents its use as a de facto mobile telecommunicationsdevice without the expensive additional hardware. In addition, thepresent invention represents an advancement over the prior art becauseit is not readily susceptible to tampering, fraud, or sabotage. Theseand other benefits of the present invention will be apparent from thedetailed description of the invention hereinbelow.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures, wherein:

FIG. 1 is a block diagram of the fixed wireless network according to oneembodiment of the present invention;

FIG. 2 is a block diagram of a fixed wireless terminal for the fixedwireless network of FIG. 1 according to one embodiment of the presentinvention;

FIG. 2A is a diagram of the network of FIG. 1 wherein the DVCC oftelecommunications signals sent on digital control channels from thebase stations are used to fix the location of the fixed wirelessterminal;

FIG. 2B is a diagram of the network of FIG. 1 wherein the DVCC oftelecommunications signals sent on analog control channels from the basestations are used to fix the location of the fixed wireless terminal;

FIG. 2C is a diagram of the network of FIG. 1 wherein the SAT oftelecommunications signals sent on analog voice channels from the basestations are used to fix the location of the fixed wireless terminal;

FIG. 3 is a block diagram of the process flow through a controller ofthe fixed wireless terminal of FIG. 2 according to one embodiment of thepresent invention;

FIG. 4 is a block diagram of the process flow through the controller ofthe fixed wireless terminal of FIG. 2 according to another embodiment ofthe present invention; and

FIG. 5 is a block diagram of the process flow through the controller ofthe fixed wireless terminal of FIG. 2 according to another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for purposes of clarity, other elements found in a typical fixedwireless terminal or fixed wireless network. For example, specificoperating system details and modules contained in the controller of thefixed wireless terminal are not shown. Those of ordinary skill in theart will recognize that these and other elements may be desirable toproduce a system incorporating the present invention. However, becausesuch elements are well known in the art, and because they do notfacilitate a better understanding of the present invention, a discussionof such elements is not provided herein.

FIG. 1 is a block diagram illustrating a typical fixed wireless network10. The network includes a subscriber unit 12, a fixed wireless terminal(FWT) 14, a number of base stations (BS₁-BS_(x)) 16, a mobile switchingcenter (MSC) 18, and a public switched telephone network (PSTN) 20. Thebase stations 16, MSC 18, and PSTN 20 may be considered to comprise amobile network, inasmuch as they support mobile telecommunications. Thesubscriber unit 12 may be any wireless telecommunications deviceincluding, for example, a telephone, telecopier, or modem. Thesubscriber unit 12 may communicate with the fixed wireless terminal 14by, for example, conventional twisted pair wiring or radio signals. Thefixed wireless terminal 14 is the interface between the subscriber unit12 and the mobile network. The fixed wireless terminal 14 receivestelecommunication signals from and transmits telecommunication signalsto the base stations 16 according to an air-interface communicationscheme such as, for example, cellular analog, FDMA, TDMA, CDMA, or GSM.Associated with each base station 16 is a cell site for which the basestation 16 provides wireless coverage. The base stations 16 and FWT 14can communicate over many different channels so that each base station16 may simultaneously communicate with many FWTs 14 within the cellsite. Cell sites often overlap and may change configurations with usagepatterns or weather conditions. The base stations 16 communicate withthe MSC 18 by, for example, an SS7 switching trunk network or an ISDN(integrated service digital network). The MSC 28 may communicate withthe PSTN 20 by, for example, an SS7 switching trunk network, an ISDN, ora TCP/IP network.

The fixed wireless network 10 may be implemented in areas where landlineservice does not exist or is inadequate. Accordingly, a user of thesubscriber unit 12 is provided telecommunications service through thewireless network via the fixed wireless terminal 14. Fixed wirelessusers of the network 10 may be charged less than mobile users. Because,however, the fixed wireless terminal 14 is a wireless telecommunicationsdevice, a user could realize mobile functionality at fixed wire rates bytransporting the fixed wireless terminal 14 between various geographiclocations. Therefore, it is typically necessary to fix the location ofthe fixed wireless terminal 14, such that a user may only achievewireless functionality from a single or fixed location. Typically, fixedwireless terminals 14 are mounted to sides of buildings or in attics,basements, and equipment rooms. The desired fixed location of a fixedwireless terminal 14 may be within only a single cell site, or it may bein a location serviced by a number of cell sites. The present inventionis directed to a method and an apparatus for determining the location ofthe fixed wireless terminal 14.

FIG. 2 is a block diagram of the fixed wireless terminal 14 of FIG. 1according to one embodiment of the present invention. The fixed wirelessterminal 14 includes an antenna 20, a transceiver 22, an interface 24,and a controller 26. The antenna 20 is for receiving and transmittingtelecommunication signals to and from the base stations 16.Alternatively, the fixed wireless terminal 14 may include a differentnumber of antennas 20, such as two antennas, wherein one antenna is fortransmitting signals and one antenna is for receiving signals. Thetransceiver 22 receives information, via the antenna 20, such as voiceand data information, transmitted by the base stations 16 modulatedaccording to the air-interface communication scheme employed by thefixed wireless network 10. For example, if the fixed wireless network 10uses TDMA, the transceiver 22 is a TDMA compliant transceiver. Theinterface 24 is in communication with the transceiver 22, and providesprotocol and/or signal format conversion between the subscriber unit 12and the transceiver 22.

The controller 26 is in communication with the transceiver 22 and theinterface 24 and may be implemented as, for example, a microprocessor,an application specific integrated circuit (ASIC), or a personalcomputer. The controller 26 includes a topology generation module 30 anda topology verification module 32, which may be implemented using anytype of computer instruction, such as microcode, and can be stored in,for example, an electrically erasable programmable read only memory(EEPROM) or can be configured into the logic of the controller 26. Themodules 30 and 32 may alternatively be implemented as software code tobe executed by the controller 26 using any suitable computer language,such as C or C++ using, for example, conventional or object-orientedtechniques. The software code may be stored as a series of instructionsor commands on a computer-readable medium, such as a random accessmemory (RAM), a read-only memory (ROM), magnetic media such as ahard-drive or a floppy disk, or optical media such as a CD-ROM.

Each cell site typically has a unique identification code sent with thetelecommunication signals transmitted to and from the base station 16providing coverage for the particular cell site. The identificationcodes are used to distinguish the telecommunications signals transmittedto and from one base station 16 from the signals transmitted to and fromother base stations 16. The identification codes may only be sent withsignals transmitted over certain channels. Such identificationmechanisms are necessary for most wireless networks to ensure that thecorrect mobile systems unit is in communication with the proper basestation 16 given that mobile networks typically require the multiplexingof numerous signals onto a single channel.

According to one embodiment of the present invention, the topologygeneration module 30 generates models of the external networkenvironment of the FWT 14 based on the identification codes in thetelecommunications signals received from the base stations 16. Thetopology generation module 30 may generate the models by scanning thesignal channels, which carry signals from one or more base stations 16,and recording the signal strength and identification codes for each ofthe scanned channels. The identification codes may only be recorded forsignals above a certain threshold signal strength. The model may, forexample, be embodied as a table containing the strength andidentification code for the signals received at each channel. Theparticular signals received will depend on the location of the FWT 14.

The topology generation module 30 may generate the network environmentmodel based different types of identification codes. For example, for adigital network, each base station 16 may transmit its own uniqueidentifying digital verification color code (DVCC) with signalstransmitted over its control channels. A DVCC is typically an 8-bit codetransmitted by a base station 16 and used to generate a coded digitalverification color code (CDVCC). The CDVCC is typically a 12-bit datafield containing the 8-bit DVCC and four protection bits, sent in eachtime slot to and from mobile stations, such as the fixed wirelessterminal 14. Because the DVCC is typically 8-bits, up to 256 unique cellsite identifying codes may be used, although typically some codes, sucha 00000000, are not used. Thus, for a digital network, the topologygeneration module 30 may generate models of the network environment ofthe fixed wireless terminal 14 by associating each received signal on acontrol channel with the DVCC sent with the signal.

FIG. 2A is a diagram of a portion of the network 10 according to such anembodiment using the DVCC of the telecommunications signals from thebase stations 16 to fix the location of the FWT 14. According to such anembodiment, the FWT 14 assembles a table of probable control channelsthat normally would be used digital control channels according to, forexample, IS-136. The FWT 14 may have a receiver sensitivity (SINAD) of;for example, −116 dBm. Table 1 is an example network environment modelof the FWT 14 at position 1 in FIG. 2A according to such as embodiment.

TABLE 1 Channel DVCC 641 71 642 50 643 97 644 23 645 N/A 646 02 647 N/A648 N/A 649 N/A 650 N/A

At position 1, for example, the FWT 14 is unable to receive and decodethe telecommunications signals on channel 646, from BS 16 ₆, because thesignal strength is lower than necessary for adequate demodulation. TheFWT 14 is unable to receive and demodulate the second appearances ofchannels 641 and 642 due to the distance from the base stations and dueto the local signals from BS 16 ₁ and BS 16 ₂.

Table 2 is an example of a network environment model of the FWT 14 atposition 2 in FIG. 2A.

TABLE 2 Channel DVCC 641 201 642 121 643 N/A 644  23 645 N/A 646  02 647N/A 648 N/A 649 N/A 650 N/A

At position 2, for example, the FWT 14 is unable to receive and decodethe telecommunications signals on channel 643 from BS 16 ₃ because thesignal strength is lower than necessary for adequate demodulation. Inaddition, the FWT 14 is unable to receive and demodulate the firstappearances of channels 641 and 642 due to the distance from the basestations and due to the local signals from BS 16 ₅ and BS 16 ₇.

According to another embodiment, each base station 16 may transmit itsown unique identifying digital color code (DCC) with telecommunicationsignals transmitted on all forward analog control channels to detectcapture of a base station by an interfering mobile station. Thus, thetopology generation module 30 may generate models of the networkenvironment by associating each received telecommunication signal on ananalog control channel with the DCC sent with the signal.

FIG. 2B is a diagram of a portion of the network 10 according to such anembodiment, wherein the DCC of the telecommunications signals from thebase stations 16 are used to fix the location of the FWT 14. Accordingto such an embodiment, the FWT 14 may assemble a table of all controlchannels that are normally used as conventional analog cellular controlchannels. The FWT 14 may have a receiver sensitivity (SINAD) of, forexample, −116 dBm. Table 3 is an example of a network environment modelof the FWT 14 at position 1 in FIG. 2B.

TABLE 3 Channel DCC Signal Strength (dBm) 334 (#1) 01 −90 335 10 −97 33610 −70 337 11 −90 338 11 −117 334 (#2) 10 −110 339 N/A N/A 340 N/A N/A341 N/A N/A 342 N/A N/A 343 N/A N/A 344 N/A N/A 345 N/A N/A 346 N/A N/A347 N/A N/A 348 N/A N/A 349 N/A N/A 350 N/A N/A 351 N/A N/A 352 N/A N/A354 N/A N/A

At position 1, for example, the FWT 14 is unable to receive and decodethe telecommunications signals on channel 338 from BS 16 ₅ because thesignal strength is lower than necessary for adequate demodulation. Inaddition, the FWT 14 is unable to receive and decode thetelecommunications signals on channel 334 (#2) from BS 16 ₆ because thechannel 334 from BS 16 ₁ is utilized on a cell site closer to the FWT14.

Table 4 is an example of a network environment model of the FWT 14 atposition 2 in FIG. 2B.

TABLE 4 Channel DCC Signal Strength (dBm) 334 (#1) 01 −111 335 10 −117336 10 −95 337 11 −71 338 11 −75 334 (#2) 10 −80 339 N/A N/A 340 N/A N/A341 N/A N/A 342 N/A N/A 343 N/A N/A 344 N/A N/A 345 N/A N/A 346 N/A N/A347 N/A N/A 348 N/A N/A 349 N/A N/A 350 N/A N/A 351 N/A N/A 352 N/A N/A354 N/A N/A

At position 2, for example, the FWT 14 is unable to receive and decodethe telecommunications signals on channel 334 from BS 16 ₂ because thesignal strength is lower than necessary for adequate demodulation. Inaddition, at position 2, the DCC for channel 334 has changed from “01”to “10” because BS 16 ₆ is physically closer to the FWT 14 than BS 16 ₁.Also, a new channel (338 from BS 16 ₅) is within range of the FWT 14 atposition 2, and another channel (335 from BS 16 ₂) is no longer withinrange.

According to another embodiment, each base station 16 may transmit itsown unique analog color code or supervisory audio tone (SAT) withtelecommunication signals on analog voice channels to identify the cell.An SAT may be comprised of different tones transmitted by the basestation 16 such as, for example, three different tones and a no-tone,for a total of four different code tones. For such an embodiment, thetopology generation module 30 may generate models of the networkenvironment by associating each received signal on an analog voicechannel above a threshold signal strength with the SAT sent with thesignal. Those and other features of the signals received by the FWT 14may be used to generate the network environment model.

FIG. 2C is a diagram of a portion of the network 10 according to such anembodiment, wherein the SAT of the telecommunications signals from thebase stations 16 are used to fix the location of the FWT 14. Accordingto such an embodiment, the voice channels may be assigned to cells asfollows:

BS 16 ₁: FOCC=334, FVC=355, 362, 369, 376, 383, 390, 397, 404, SAT=5970

BS 16 ₂: FOCC=335, FVC=356, 363, 370, 377, 384, 391, 398, 405, SAT=6000

BS 16 ₃: FOCC=336, FVC=357, 364, 371, 378, 385, 392, 399, 406, SAT=6000

BS 16 ₄: FOCC=337, FVC=348, 365, 372, 379, 386, 393, 400, 407, SAT=6030

BS 16 ₅: FOCC=335, FVC=356, 363, 370, 377, 384, 391, 398, 405, SAT=6030

BS 16 ₆: FOCC=334, FVC=355, 362, 369, 376, 383, 390, 397, 404, SAT=6000

According to this scenario, the value of the threshold signal strengthmay be set at, for example, −95 dBm. The FWT 14 may generate a tablewith every voice channel within the assigned band plan. For a B Band UScellular wireless network, those channels range from channel number 355to 666, and 717 to 799.

Table 5 is an example of a network environment model of the FWT 14 atposition 1 in FIG. 2C, although some of the channels are not included,and wherein SAT 0=no tone, SAT 1=5970, SAT 2=6000, and SAT 3=6030.

TABLE 5 Channel SAT 355 1 356 2 357 2 358 3 359 N/A 360 N/A 361 N/A 3621 363 2 364 2 365 3 366 N/A 367 N/A 368 N/A 369 1 370 2 371 2 372 3 373N/A 374 N/A 375 N/A 376 1 377 2 378 2 379 3 380 N/A 381 N/A 382 N/A 383N/A 384 1 385 2 386 2 387 3 388 N/A 389 N/A 390 1 391 2 392 2 393 3 394N/A 395 N/A 396 N/A 397 1 398 2 399 2 400 3 401 N/A 402 N/A 403 N/A 4041 405 1 406 2 407 3

Table 6 is an example of the network environment of the FWT 14 atposition 2 of FIG. 2C

TABLE 6 Channel SAT 355 2 356 3 357 2 358 3 359 N/A 360 N/A 361 N/A 3622 363 3 364 2 365 3 366 N/A 367 N/A 368 N/A 369 2 370 3 371 2 372 3 373N/A 374 N/A 375 N/A 376 2 377 3 378 2 379 3 380 N/A 381 N/A 382 N/A 3832 384 3 385 2 386 3 387 N/A 388 N/A 389 N/A 390 2 391 3 392 2 393 3 394N/A 395 N/A 396 N/A 397 2 398 3 399 2 400 3 401 N/A 402 N/A 403 N/A 4042 405 3 406 2 407 3

As is seen by comparing the models shown in Tables 5 and 6, manydifferences exist therebetween. These differences may be used by thetopology verification module 32 to determine whether position 1 is thesame as position 2, as described hereinbelow.

The topology generation module 30 may store an initial model of thenetwork environment in a memory, such as the internal memory of thecontroller 26 or a peripheral memory device. According to one embodimentof the present invention, the topology generation module 30 generatesthe initial model of the network environment when the fixed wirelessterminal 14 is physically located in its desired fixed location. Thetopology generation module 30 may also rescan the channels periodicallyto generate current models of the network environment of the fixedwireless terminal 14. The topology generation module 30 may rescan theenvironment with enough periodicity to minimize potential fraudulent orabusive use of the mobile qualities of the fixed wireless terminal 14.For example, the topology generation module 30 may rescan the networkenvironment of the fixed wireless terminal 14 every hour. According toanother embodiment, the network environment is rescanned every time thesubscriber unit 12 is activated, indicating that a user of thesubscriber unit 12 may seek to be connected to the wireless network 10.

The topology verification module 32 is in communication with thetopology generation module 30 and compares the generated models of thenetwork environment. For example, the topology verification module 32may compare a current model of the network environment with a previouslygenerated model. The topology verification module 32 may compare themodels by, for example, comparing the identification codes stored in themodels. If the identification codes for a predetermined number ofsignals for the actual network environment are different than theidentification codes for the previously generated model, the topologyverification module 32 may determine that the fixed wireless terminal 14is not located in the same physical location as it was located when theprevious model was generated. According to one embodiment, the topologyverification module 32 may determine that the FWT 14 is not in the samelocation if, for example, more than 20% of the identification codescomprising the models are different. If the topology verification module32 determines that the fixed wireless terminal 14 is not located in itsprevious location (i.e., if the topology verification module 32determines that the fixed wireless terminal 14 is mobile), the topologyverification module 32 may establish a remedy such as, for example,denying a user of the subscriber unit 12 access to the network for apredetermined period of time. The topology verification module 32 mayallow for more than one determination that the fixed wireless terminal14 is mobile before initiating remedial actions. For example, if thetopology verification module 32 determines that the channelidentification codes are different on two different scans within sixmonths, the topology verification module 32 may deny the fixed wirelessuser access to the network for a period of time, such as twenty-fourhours. To support emergency communications, however, the topologyverification module 32 may nevertheless permit access to the fixedwireless network 10 if the topology verification module 32 recognizesthe attempted access as a recognized emergency, such as if a user calls“911” in the United States.

FIG. 3 is a diagram illustrating a process flow through the controller26 according to one embodiment of the present invention. The processflow begins at block 40, where a first model of the network environmentof the fixed wireless terminal 14 is generated based on theidentification codes. For example, the first network environment modelmay be constructed from the identification codes of the signalstransmitted over certain channels, such as the DCC for analog controlchannels, the DVCC for digital control channels, or the SAT for analogvoice channels. As discussed hereinbefore, the first model may begenerated when the fixed wireless terminal 14 is located in its desiredphysical location. From block 40, the process flow continues to block42, where an internal counter is set to zero.

From block 42, the process flow advances to block 44, where a secondmodel of the network environment is generated. The second model may begenerated, for example, a predetermined period of time after the firstmodel is generated. Alternatively, the second model may be generatedwhen the subscriber unit 12 is activated.

From block 44, the process flow advances to block 46, where the firstand second network environment models are compared. If the second modelsufficiently matches the first model, it is determined that the fixedwireless terminal 14 is likely in the same location as it was when thefirst model was generated, and the process flow advances to block 48,where the subscriber is permitted to access the fixed wireless network10. Conversely, if at block 46 it is determined that the models do notsufficiently match, it is assumed that the fixed wireless terminal 14 isnot in the same location as when the first model was generated (i.e.,the fixed wireless terminal 14 is mobile), and the process flow proceedsto block 50. Whether the models sufficiently match may be determinedbased, for example, on whether the identification codes of apredetermined number of signals match. According to one embodiment,complete identity between the identification codes is not required so asto minimize the likelihood of false determinations that the fixedwireless terminal 14 is mobile, such as may be caused byreconfigurations of the cells or changing weather phenomena. For such anembodiment, the predetermined threshold may be set to allow for somevariation but to reasonably ensure that the fixed wireless terminal 14is in approximately the same location as it was when the first model wasgenerated. For example, the models may be determined to not sufficientlymatch where they differ by more than, for example, 20%.

At block 50, the internal counter is incremented by one unit. Thenumerical quantity of the counter represents the number of times that ithas been determined that the fixed wireless terminal 14 is mobile. Theprocess flow then proceeds to block 52, where the value of the counteris checked If the counter is equal to one, the process flow returns toblock 48, and the subscriber is permitted to access the network Thus,according to the illustrated process flow, access to the network isstill permitted despite the fact that on one occasion it has beendetermined that the fixed wireless terminal 14 is mobile. Conversely, ifthe counter does not equal one, e.g., if it equals two, the process flowproceeds to block 54.

At block 54, even though the counter is greater than one, the subscribermay nevertheless be permitted to access the network under certaincircumstances, such as for emergency purposes. Thus, at block 54, it isdetermined whether the user of the subscriber unit 12 is seeking toaccess the network for an identifiable potential emergency purpose, suchas if the user of the subscriber unit 12 calls “911” in the UnitedStates. If so, the flow proceeds to block 48, and the user is permittedto access the network. Conversely, if the counter does not equal one andaccess to the network is being sought for other than identifiableemergency purposes, the process flow proceeds to block 56.

At block 56, a remedy is established because the fixed wireless terminal14 has been determined to be mobile on at least two occasions. Accordingto the illustrated embodiment, the remedy is disabling the subscriberunit 12 from accessing the fixed wireless network 10. According to oneembodiment, any user of the subscriber unit 12 would be denied accessfor a predetermined period of time, such as twenty-four hours. Fromblock 56, the process flow returns to block 42, where the counter isreset to zero, and a subsequent model of the network environment isgenerated to be compared to the first model.

From block 48, the process flow proceeds to block 58, where it isdetermined whether the counter was last incremented more than six monthsago. If the counter was last incremented more than six months ago, theprocess flow returns to block 42, where the counter is reset to zero.Conversely, if the counter was last incremented less than six monthsago, the process flow returns to block 44, therefore not causing thecounter to be reset to zero prior to the generation of a subsequentnetwork environment of the fixed wireless terminal 14. Thus, accordingto the illustrated embodiment, the subscriber unit 12 is only disabledfrom the fixed wireless network 10 if it is determined that the fixedwireless terminal 14 is mobile on at least two occasions within a sixmonth time frame.

Other embodiments of the present invention include variations on theembodiment of the process flow illustrated in FIG. 3. For example, asubscriber may be denied access to the network the first time the fixedwireless terminal 14 is determined not to be in its desired location,i.e., when the counter reaches one. In addition, after disabling thesubscriber from the network after two determinations that the fixedwireless terminal 14 is mobile, the counter may be reset to one, ratherthan zero. In addition, at block 58, the time frame could be other thansix months, such as one year. Further, the remedy could be other thandisabling the subscriber from the network for a period time. Forexample, the remedy may be a surcharge stipulated in the subscriberservice contract. According to another embodiment, the remedy may be tocharge the subscriber for mobile rates while the fixed wireless network14 is mobile, rather than the typically lower fixed wire rates.

According to another embodiment of the present invention, the controller26 may determine whether the fixed wireless terminal 14 is located in aspecific location by monitoring the time of arrival (TOA) oftelecommunication signals received from the base stations 16. Forexample, the fixed wireless terminal 14 may include two antennas 20located a fixed, known distance apart. The topology generation module 30may determine the direction of the fixed wireless terminal 14 relativeto a particular base station 16 based on the TOA between signalsreceived by the respective antennas 20 from the base station 16. Bydetermining the direction of the fixed wireless terminal 14 relative toan additional base station 16 which is geographically dispersed from thefirst base station 16, the topology generation module 30 may fix thelocation of the fixed wireless terminal 14. The topology verificationmodule 32 may compare the current determined location of the fixedwireless terminal 14 as determined by the topology generation module 30with a prior determined location to determine if the fixed wirelessterminal 14 is in the same location or if it is mobile.

According to another embodiment of the present invention, the fixedwireless terminal 14 has one antenna 20, and the controller 26determines the location of the fixed wireless terminal 14 based on theTOA of received signals transmitted synchronously from at least two basestations 16, such as may be used for certain TDMA-based networks.According to such an embodiment, because the telecommunication signalstransmitted from the base stations 16 are synchronized, the time ofarrival of the signals from the different base stations 16 is indicativeof the fixed wireless terminal's location relative to the base stations16.

FIG. 4 is a diagram illustrating a process flow through the controller26 according to one embodiment of the present invention in which TOA isused to generate the models of the network environment. The process flowillustrated in FIG. 4 is similar to that illustrated in FIG. 3, exceptat blocks 60 and 62 the models of the network environment are generatedbased on TOA between received telecommunication signals. In addition, atblock 66, the estimated positions of the fixed wireless terminal 14 foreach model is compared.

According to another embodiment of the present invention, the controller26 may fix the location of the fixed wireless terminal 14 by monitoringthe received signal strengths (RSSI) of telecommunication signalsreceived by the fixed wireless terminal 14 from the base stations 16.For such an embodiment, the topology generation module 30 may generatemodels of the network environment by scanning a number of channels fromone or more base stations 16 and associating the RSSI of the receivedsignal with each the scanned channels. The model may, for example,include a table identifying the RSSI for each received signal above aparticular threshold signal strength and the channel on which the signalwas received. The topology verification module 32 may fix the locationof the fixed wireless terminal 14 by comparing the network environmentmodels generated by the topology generation module 30 based on the RSSIof the received signals.

FIG. 5 is a diagram illustrating a process flow through the controller26 according to one embodiment of the present invention in which RSSI isused to generate the models of the network environment. The process flowillustrated in FIG. 5 is similar to that illustrated in FIG. 3, exceptthat at blocks 70 and 72 the models of the network environment aregenerated based on the RSSI of the received telecommunication signals.In addition, at block 74, the network environment models generatedaccording to the RSSI are compared.

While the present invention has been described in conjunction withcertain embodiments thereof, many modifications and variations will beapparent to those of ordinary skill in the art. For example, the flowthrough modules 30 and 32 may be alternatively arranged to still realizethe benefit of the present invention. Furthermore, although theinvention has been described in terms of a fixed wireless system, thepresent invention may be embodied in mobile wireless systems. Forexample, in a mobile wireless system in which usage is restricted orfees vary based on the locations of the user. The foregoing descriptionand the following claims are intended to cover all such modificationsand variations.

What is claimed is:
 1. A method for fixing a location of a transportablefixed wireless terminal in a fixed wireless network, comprising: at thetransportable fixed wireless terminal: receiving telecommunicationsignals transmitted from a first set of base stations; generating afirst model of a network environment of the transportable fixed wirelessterminal based on the telecommunication signals received from the firstset of base stations; receiving telecommunication signals transmittedfrom a second set of base stations; generating a second model of thenetwork environment of the transportable fixed wireless terminal basedon the telecommunication signals received from the second set of basestations; and determining whether the first and second models differbeyond a predetermined limit.
 2. The method of claim 1, wherein:generating the first model includes generating the first model of thenetwork environment based on a first set of identification codes in thetelecommunication signals received from the first set of base stations,wherein each identification code in the first set of identificationcodes is indicative of a different base station included in the firstset of base stations; and generating the second model includesgenerating the second model of the network environment based on a secondset of identification codes in the telecommunication signals receivedfrom the second set of base stations, wherein each identification codein the second set of identification codes is indicative of a differentbase station included in the second set of base stations.
 3. The methodof claim 2, wherein determining whether the first and second modelsdiffer beyond a predetermined limit includes comparing the first set ofidentification codes with the second set of identification codes.
 4. Themethod of claim 2, wherein: generating the first model includesgenerating the first model of the network environment based on a firstset of digital verification color codes in the telecommunication signalsreceived from the first set of base stations; and generating the secondmodel includes generating the second model of the network environmentbased on a second set of digital verification color codes in thetelecommunication signals received from the second set of base stations.5. The method of claim 2, wherein: generating the first model includesgenerating the first model of the network environment based on a firstset of digital color codes in the telecommunication signals receivedfrom the first set of base stations; and generating the second modelincludes generating the second model of the network environment based ona second set of digital color codes in the telecommunication signalsreceived from the second set of base stations.
 6. The method of claim 2,wherein: generating the first model includes generating the first modelof the network environment based on a first set of supervisory audiotones in the telecommunication signals received from the first set ofbase stations; and generating the second model includes generating thesecond model of the network environment based on a second set ofsupervisory audio tones in the telecommunication signals received fromthe second set of base stations.
 7. The method of claim 1, wherein:generating the first model includes generating the first model based ona first set of received signal strengths for the telecommunicationsignals received from the first set of base stations; and generating thesecond model includes generating the second model based on a second setof received signal strengths for the telecommunication signals receivedfrom the second set of base stations.
 8. The method of claim 1, wherein:generating the first model includes generating the first model based ona first set of arrival times for the telecommunication signals receivedfrom the first set of base stations; and generating the second modelincludes generating-the second model based on a second set of arrivaltimes for the telecommunication signals received from the second set ofbase stations.
 9. The method of claim 1, further comprising establishinga remedy when the first and second network environment models differbeyond the predetermined limit.
 10. The method of claim 9, whereinestablishing a remedy includes preventing a user of the fixed wirelessterminal from accessing the fixed wireless network.
 11. The method ofclaim 10, wherein preventing a user from accessing the fixed wirelessnetwork includes preventing the user from accessing the fixed wirelessnetwork for a predetermined period of time.
 12. A transportable fixedwireless terminal, comprising: a transceiver for receivingtelecommunication signals from one or more base stations; an interfacein communication with the transceiver; a topology generation module incommunication with the transceiver for generating first and secondmodels of a network environment of the transportable fixed wirelessterminal based on telecommunication signals received from the one ormore base stations; and a topology verification module in communicationwith the topology generation module for comparing the first and secondmodels.
 13. The fixed wireless terminal of claim 12, wherein thetopology generation module generates the first and second models basedon a characteristic of each of the telecommunication signals receivedfrom the one or more base stations, the characteristic selected from thegroup consisting of a received signal strength, a time of arrival, andan identification code, wherein the identification code is indicative ofa base station from which the received signal was transmitted.
 14. Thefixed wireless terminal of claim 13, wherein the identification code isselected from the group consisting of a digital verification color code,a digital color code, and a supervisory audio tone.
 15. The fixedwireless terminal of claim 12, wherein the topology verification moduleestablishes a remedy when the first model and the second model differbeyond a predetermined limit.
 16. A transportable fixed wirelessterminal, comprising: a transceiver for receiving telecommunicationsignals from one or more base stations; by an interface in communicationwith the transceiver; and a controller in communication with thetransceiver and the interface, the controller including acomputer-readable medium, having stored thereon instructions, which whenexecuted by the controller, cause the controller to: generate first andsecond models of a network environment of the transportable fixedwireless terminal based on telecommunication signals received from theone or more base stations; and compare the first and second models. 17.The fixed wireless terminal of claim 16, wherein the computer-readablemedium has stored thereon instructions, which when executed by thecontroller, cause the controller to generate the first and second modelsbased on a characteristic of each of the telecommunication signalsreceived from the one or more base stations, the characteristic selectedfrom the group consisting of a received signal strength, a time ofarrival, and an identification code, wherein the identification code isindicative of a base station from which the received signal wastransmitted.
 18. The fixed wireless terminal of claim 17, wherein theidentification code is selected from the group consisting of a digitalverification color code, a digital color code, and a supervisory audiotone.
 19. A wireless network, comprising: a mobile switching center; aplurality of base stations in communication with the mobile switchingcenter; and a transportable fixed wireless terminal in communicationwith one or more of the plurality of base stations, wherein thetransportable fixed wireless terminal includes: a transceiver forreceiving telecommunication signals from the one or more base stations;an interface in communication with the transceiver; a topologygeneration module in communication with the transceiver for generatingfirst and second models of a network environment of the transportablefixed wireless terminal based on telecommunication signals received fromthe one or more base stations; and a topology verification module incommunication with the topology generation module for comparing thefirst and second models.
 20. The network of claim 19, wherein the mobileswitching center is in communication with a public switched telephonenetwork.
 21. The network of claim 19, wherein the topology generationmodule generates the first and second models based on a characteristicof each of the telecommunication signals received from the one or morebase stations, the characteristic selected from the group consisting ofa received signal strength, a time of arrival, and an identificationcode, wherein the identification code is indicative of a base stationfrom which the received signal was transmitted.
 22. The network of claim21, wherein the identification code is selected from the groupconsisting of a digital verification color code, a digital color code,and a supervisory audio tone.
 23. The network of claim 19, wherein thetopology verification module establishes a remedy when the first modeland the second model differ beyond a predetermined limit.